Through the Internet, web providers have made many types of web-based resources freely available to users, such as email accounts, search services, and instant messaging. Unfortunately, malicious entities may take advantage of freely available resources to use them for illegitimate and undesirable purposes, such as spamming, web attacks, and distribution of malicious software applications. To frustrate the efforts of these malicious entities, Human Interactive Proofs (HIPs) have been employed to selectively provide access to resources when the HIP determines that a given interaction came from a human. Doing so creates barriers to malicious entities that make use of automated systems to abuse or overuse freely available resources.
One traditional technique for a human interactive proof involves presenting a text-based puzzle. This technique involves challenging a computing device (e.g., a client) with a text-based puzzle when the computing device attempts to access resources. Typically, the answer to the puzzle is text within the puzzle that has been obfuscated in some manner to make it difficult for a computer to recognize. Recently, improvements in optical character recognition (OCR) as well as malicious attacks from “sweatshops” have all but defeated the viability of the traditional text-based puzzles for HIP. Accordingly, some traditional HIP techniques may no longer be capable of creating a successful barrier to malicious entities.